1. Field of the Invention
The present invention relates to pressure operated safety valves for disposition in well tubing.
2. Description of the Prior Art
In the past, it has been the practice to use devices in producing wells, particularly offshore wells, which automatically close when the well pressure reaches a predetermined amount for the purpose of preventing well blowouts and the resultant fires and pollution of the sea with oil.
The most common type has been marketed under the name "storm" choke, but it is not as widely used as it should be because it is generally damaged by sand or other abrasives flowing therethrough with the oil during normal production, so that it is not operative for preventing blowouts when they occur.
Ball-type safety valves, examples of which are found in U.S. Pat. Nos. 2,894,715; Re25,471; 2,998,070; 3,035,808; 3,126,908 3,189,044 and 3,059,913 have also been used in an attempt to provide automatic closing of wells to prevent well blowouts. However, even the best of the safety valves are subject to malfunctioning, particularly after having been left in a well for a period of time. Since the government requires periodic testing of the safety valves, those that are defective can be located, but with the previously known valves, even if they were found to be defective, nothing could be done to immobilize or replace the defective valve, short of shutting down the well and attempting a removal of the defective valve with all of the attendant problems.